Heat Shocking the Jedi Master: HSP90's Role in Regulating Stomatal Cell Fate

Transcriptome Analysis of Jujube (Ziziphus jujuba Mill.) Response to Heat Stress

Heat stress (HS) is a common stress influencing the growth and reproduction of plant species. Jujube (Ziziphus jujuba Mill.) is an economically important tree with strong abiotic stress resistance, but the molecular mechanism of its response to HS remains elusive. In this study, we subjected seedlings of Z. jujuba cultivar “Hqing1-HR” to HS (45°C) for 0, 1, 3, 5, and 7 days, respectively, and collected the leaf samples (HR0, HR1, HR3, HR5, and HR7) accordingly. Fifteen cDNA libraries from leaves were constructed for transcriptomics assays. RNA sequencing and transcriptomics identified 1,642, 4,080, 5,160, and 2,119 differentially expressed genes (DEGs) in comparisons of HR1 vs. HR0, HR3 vs. HR0, HR5 vs. HR0, and HR7 vs. HR0, respectively. Gene ontology analyses of the DEGs from these comparisons revealed enrichment in a series of biological processes involved in stress responses, photosynthesis, and metabolism, suggesting that lowering or upregulating expression of these genes might play important roles in the response to HS. This study contributed to our understanding of the molecular mechanism of jujube response to HS and will be beneficial for developing jujube cultivars with improved heat resistance.

HSP90 chaperones regulate stomatal differentiation under normal and heat stress conditions

Stomatal development is tightly connected with the overall plant growth, while changes in environmental conditions, like elevated temperature, affect negatively stomatal formation. Stomatal ontogenesis follows a well-defined series of cell developmental transitions in the cotyledon and leaf epidermis that finally lead to the production of mature stomata. YODA signaling cascade regulates stomatal development mainly through the phosphorylation and inactivation of SPEECHLESS (SPCH) transcription factor, while HSP90 chaperones have a central role in the regulation of YODA cascade. Here, we report that acute heat stress affects negatively stomatal differentiation, leads to high phosphorylation levels of MPK3 and MPK6, and alters the expression of SPCH and MUTE transcription factors. Genetic depletion of HSP90 leads to decreased stomatal differentiation rates. Thus, HSP90 chaperones safeguard the completion of distinct stomatal differentiation steps depending on these two transcription factors under normal and heat stress conditions.